http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Bright visible light emission from graphene
Kim, Young Duck,Kim, Hakseong,Cho, Yujin,Ryoo, Ji Hoon,Park, Cheol-Hwan,Kim, Pilkwang,Kim, Yong Seung,Lee, Sunwoo,Li, Yilei,Park, Seung-Nam,Shim Yoo, Yong,Yoon, Duhee,Dorgan, Vincent E.,Pop, Eric,Hein Nature Publishing Group 2015 Nature nanotechnology Vol.10 No.8
Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible and transparent optoelectronics. In particular, the strong light–matter interaction in graphene has allowed for the development of state-of-the-art photodetectors, optical modulators and plasmonic devices. In addition, electrically biased graphene on SiO<SUB>2</SUB> substrates can be used as a low-efficiency emitter in the mid-infrared range. However, emission in the visible range has remained elusive. Here, we report the observation of bright visible light emission from electrically biased suspended graphene devices. In these devices, heat transport is greatly reduced. Hot electrons (∼2,800 K) therefore become spatially localized at the centre of the graphene layer, resulting in a 1,000-fold enhancement in thermal radiation efficiency. Moreover, strong optical interference between the suspended graphene and substrate can be used to tune the emission spectrum. We also demonstrate the scalability of this technique by realizing arrays of chemical-vapour-deposited graphene light emitters. These results pave the way towards the realization of commercially viable large-scale, atomically thin, flexible and transparent light emitters and displays with low operation voltage and graphene-based on-chip ultrafast optical communications.
Focused-Laser-Enabled p–n Junctions in Graphene Field-Effect Transistors
Kim, Young Duck,Bae, Myung-Ho,Seo, Jung-Tak,Kim, Yong Seung,Kim, Hakseong,Lee, Jae Hong,Ahn, Joung Real,Lee, Sang Wook,Chun, Seung-Hyun,Park, Yun Daniel American Chemical Society 2013 ACS NANO Vol.7 No.7
<P>With its electrical carrier type as well as carrier densities highly sensitive to light, graphene is potentially an ideal candidate for many optoelectronic applications. Beyond the direct light–graphene interactions, indirect effects arising from induced charge traps underneath the photoactive graphene arising from light–substrate interactions must be better understood and harnessed. Here, we study the local doping effect in graphene using focused-laser irradiation, which governs the trapping and ejecting behavior of the charge trap sites in the gate oxide. The local doping effect in graphene is manifested by large Dirac voltage shifts and/or double Dirac peaks from the electrical measurements and a strong photocurrent response due to the formation of a p–n–p junction in gate-dependent scanning photocurrent microscopy. The technique of focused-laser irradiation on a graphene device suggests a new method to control the charge-carrier type and carrier concentration in graphene in a nonintrusive manner as well as elucidate strong light–substrate interactions in the ultimate performance of graphene devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-7/nn402354j/production/images/medium/nn-2013-02354j_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn402354j'>ACS Electronic Supporting Info</A></P>
Engineering Optical and Electronic Properties of WS<sub>2</sub> by Varying the Number of Layers
Kim, Hyun-Cheol,Kim, Hakseong,Lee, Jae-Ung,Lee, Han-Byeol,Choi, Doo-Hua,Lee, Jun-Ho,Lee, Wi Hyoung,Jhang, Sung Ho,Park, Bae Ho,Cheong, Hyeonsik,Lee, Sang-Wook,Chung, Hyun-Jong American Chemical Society 2015 ACS NANO Vol.9 No.7
<P>The optical constants, bandgaps, and band alignments of mono-, bi-, and trilayer WS<SUB>2</SUB> were experimentally measured, and an extraordinarily high dependency on the number of layers was revealed. The refractive indices and extinction coefficients were extracted from the optical-contrast oscillation for various thicknesses of SiO<SUB>2</SUB> on a Si substrate. The bandgaps of the few-layer WS<SUB>2</SUB> were both optically and electrically measured, indicating high exciton-binding energies. The Schottky-barrier heights (SBHs) with Au/Cr contact were also extracted, depending on the number of layers (1–28). From an engineering viewpoint, the bandgap can be modulated from 3.49 to 2.71 eV with additional layers. The SBH can also be reduced from 0.37 eV for a monolayer to 0.17 eV for 28 layers. The technique of engineering materials’ properties by modulating the number of layers opens pathways uniquely adaptable to transition-metal dichalcogenides.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-7/acsnano.5b01727/production/images/medium/nn-2015-017277_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b01727'>ACS Electronic Supporting Info</A></P>
Kim, Hakseong,Shin, Dong Hoon,McAllister, Kirstie,Seo, Miri,Lee, Sangik,Kang, Il-Suk,Park, Bae Ho,Campbell, Eleanor E. B.,Lee, Sang Wook American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.8
<P>Accurate and precise determination of mechanical properties of nanoscale materials is mandatory since device performances of nanoelectromechanical systems (NEMS) are closely related to the flexural properties of the materials. In this study, the intrinsic mechanical properties of highly stressed silicon nitride (SiN) beams of varying lengths are investigated using two different techniques: Dynamic flexural measurement using optical interferometry and quasi-static flexural measurement using atomic force microscopy. The resonance frequencies of the doubly clamped, highly stressed beams are found to be inversely proportional to their length, which is not usually observed from a beam but is expected from a string-like structure. The mass density of the SiN beams can be precisely determined from the dynamic flexural measurements by using the values for internal stress and Young's modulus determined from the quasi-static measurements. As a result, the mass resolution of the SiN beam resonators was predicted to be a few attograms, which was found to be in excellent agreement with the experimental results. This work suggests that accurate and precise determination of mechanical properties can be achieved through combined flexural measurement techniques, which is a crucial key for designing practical NEMS applications such as biomolecular sensors and gas detectors.</P>
Accurate Gap Determination in Monolayer and Bilayer Graphene/<i>h</i>-BN Moiré Superlattices
Kim, Hakseong,Leconte, Nicolas,Chittari, Bheema L.,Watanabe, Kenji,Taniguchi, Takashi,MacDonald, Allan H.,Jung, Jeil,Jung, Suyong American Chemical Society 2018 Nano letters Vol.18 No.12
<P>High mobility single and few-layer graphene sheets are in many ways attractive as nanoelectronic circuit hosts but lack energy gaps, which are essential to the operation of field-effect transistors. One of the methods used to create gaps in the spectrum of graphene systems is to form long period moiré patterns by aligning the graphene and hexagonal boron nitride (<I>h</I>-BN) substrate lattices. Here, we use planar tunneling devices with thin <I>h</I>-BN barriers to obtain direct and accurate tunneling spectroscopy measurements of the energy gaps in single-layer and bilayer graphene-<I>h</I>-BN superlattice structures at charge neutrality (first Dirac point) and at integer moiré band occupancies (second Dirac point, SDP) as a function of external electric and magnetic fields and the interface twist angle. In single-layer graphene, we find, in agreement with previous work, that gaps are formed at neutrality and at the hole-doped SDP, but not at the electron-doped SDP. Both primary and secondary gaps can be determined accurately by extrapolating Landau fan patterns to a zero magnetic field and are as large as ≈17 meV for devices in near-perfect alignment. For bilayer graphene, we find that gaps occur only at charge neutrality where they can be modified by an external electric field.</P> [FIG OMISSION]</BR>
Development of Questionnaire for Examining Science Learning Network of Elementary School Students
김영대(Youngdae Kim),김학성(Hakseong Kim) 한국교원대학교 뇌기반교육연구소 2021 Brain, Digital, & Learning Vol.11 No.4
This study developed questionnaires designed to measure student centrality and cohesion in small groups. Student centrality and small group cohesion were defined in terms of their effect on and relation to other students in a science learning network. Drafts of the questionnaire items were made, based on such operational definitions, and the questionnaire instrument composed of 6 items through 4 pilot tests and 5 validation verification. Application of the questionnaire to 168 students (42 small groups) in the sixth grade of elementary school showed that the students centrality value (0~2) reached 0.293 on average and the small group cohesion value (0~1) 0.319, respectively. Unlike cohesion that showed normal distribution, the centrality values showed a positively skewed distribution toward the left. The majority of the students tested turned out to possess centrality of an ordinary level. This study devised methods of utilizing centrality and cohesion, which are relationship features of students in a small group in scientific inquiry activities. The questionnaire that was developed measured small group centrality and cohesion is expected to apply to school education.